Combine chicken broth and garlic in a small saucepan.
Bring to boil, reduce heat to low, and simmer, covered, for 20 minutes.
Heat 1 inch of water in a steamer.
Place zucchini, yellow summer squash, and red pepper in a steamer basket or collander, cover, and steam until squash are tender.
Pour broth-garlic mixture into a blender or food processor and add balsamic vinegar.
Process until smooth.
Return to saucepan over low heat until ready to serve.
Toss together cooked pasta, steamed vegetables, scallions, cherry tomatoes, and garlic puree in a large bowl.